You can show the balance of the primary wallet by using the useDynamicContext hook and the getBalance method from the wallet connector.
React
import { useDynamicContext } from '@dynamic-labs/sdk-react-core'

const { primaryWallet } = useDynamicContext()

const [balance, setBalance] = useState(null)

useEffect(() => {
  const fetchBalance = async () => {
    if (primaryWallet) {
      const value = await primaryWallet.getBalance()
      setBalance(value)
    }
  }
  fetchBalance()
}, [primaryWallet])

return <p>{balance}</p>